Crystal oscillator control circuit and associated oscillation device

ABSTRACT

A crystal oscillator control circuit includes a first terminal and a second terminal, a current source, and a peak detection and bias voltage adjustment circuit. The first terminal and the second terminal are arranged to couple the crystal oscillator control circuit to a crystal. The current source is coupled to a power supply voltage and generates a bias current. The peak detection and bias voltage adjustment circuit is coupled between the bias current and a ground voltage and coupled to the first terminal, and performs peak detection and bias voltage adjustment to correspondingly generate a first signal at a node. The low-pass filter low-pass filters the first signal to generate a filtered signal. The feedback control circuit is arranged to perform feedback control according to the filtered signal to generate an oscillation signal at one or both of the first terminal and the second terminal.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an oscillator, and more particularly,to a crystal oscillator control circuit and associated oscillationdevice.

2. Description of the Prior Art

A crystal oscillator may use a resistor as a feedback device of a gainstage. Another option for implementing the feedback device may be ananalog switch, such as an analog Metal Oxide Semiconductor Field EffectTransistor (MOSFET) switch. When Complementary Metal-Oxide-Semiconductor(CMOS) process is applied, resistors may cause unwanted cost due tooccupying a large area, while resistance of the analog switch may besensitive to process, power supply and temperature. Further, when signalamplitude is large, the analog switch may introduce an unbalanced DCvoltage between the input and the output.

Aside from the above problems, there are further issues. In order tomake the crystal oscillator less sensitive to the Printed Circuit Board(PCB) leakage current, a related art technique suggests that an on-chipcapacitor series with a resistor may be inserted between the input andoutput. As this resistor occupies an extremely large area in a lowfrequency crystal oscillator design, however, this results in tremendousincreases in cost. In another example, the crystal oscillation amplitudemay be limited by a loop to reduce the circuit power, thus requiring anAutomatic Gain Control (AGC) loop and a low-pass filter (LPF). Accordingto the related art, this objective cannot be achieved without applying aresistor or an analog switch; thus there is a trade-off between how tosolve problems existing in the art and how to mitigate problemsnewly-introduced by the solutions.

Therefore, there is a need for a novel architecture to improve theoverall performance of an electronic system without introducing a sideeffect or in a way that less likely to introduce a side effect.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a crystal oscillatorcontrol circuit and associated oscillation device, in order to solve theabove-mentioned problems.

An objective of the present invention is to provide a crystal oscillatorcontrol circuit and associated oscillation device which can achieve anoptimal performance without introducing a side effect or in a way thatless likely to introduce a side effect.

At least one embodiment of the present invention provides a crystaloscillator control circuit. The crystal oscillator control circuitcomprises a first terminal and a second terminal, a current source, apeak detection and bias voltage adjustment circuit, a low-pass filter,and a feedback control circuit. The first terminal and the secondterminal are arranged to couple the crystal oscillator control circuitto a crystal. The current source is coupled to a power supply voltage,and arranged to generate a bias current. The peak detection and biasvoltage adjustment circuit is coupled between the bias current and aground voltage and coupled to the first terminal, and is arranged toperform peak detection and bias voltage adjustment, in order tocorrespondingly generate a first signal at a node. The low-pass filteris coupled to the node, and is arranged to low-pass filter the firstsignal in order to generate a filtered signal. The feedback controlcircuit is coupled to the low-pass filter and coupled to the firstterminal and the second terminal, and is arranged to perform feedbackcontrol according to the filtered signal in order to generate anoscillation signal at one or both of the first terminal and the secondterminal.

At least one embodiment of the present invention provides an oscillationdevice which comprises the crystal oscillator control circuit mentionedabove. The oscillation device may further comprise: the crystal coupledbetween the first terminal and the second terminal; and a firstcapacitor and a second capacitor coupled to the first terminal and thesecond terminal, respectively.

An advantage provided by the present invention is that the crystaloscillator control circuit does not need any resistor or analog switch.More particularly, the problem of unwanted area occupation ofconfiguring a feedback resistor can be avoided. In addition to the aboveadvantages, the crystal oscillator control circuit is also insensitiveto leakage current. Compared with related art, the crystal oscillatorcontrol circuit and the oscillation device of the present invention maybe implemented as a resistor-less circuit and device respectively, whilealso achieving the required functions while maintaining a considerablysmall size.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a crystal oscillator control circuitaccording to an embodiment of the present invention.

FIG. 2 illustrates an example of an oscillation device which comprisesthe crystal oscillator control circuit shown in FIG. 1.

FIG. 3 illustrates some examples of related signals of the crystaloscillator control circuit shown in FIG. 1.

DETAILED DESCRIPTION

FIG. 1 is a diagram illustrating a crystal oscillator control circuit100 according to an embodiment of the present invention. The crystaloscillator control circuit 100 may comprise terminals XTAL_I andXTAL_IO, a current source for generating a bias current IBias, a peakdetection and bias voltage adjustment circuit 110 and a low-pass filter120, and may further comprise a feedback control circuit, such as thatshown on the right side of the low-pass filter 120 within thearchitecture shown in FIG. 1, wherein the current source is coupled tothe power supply voltage VDD, and the peak detection and bias voltageadjustment circuit 110 is coupled between the bias current IBias and theground voltage VSS, and may be coupled to the terminal XTAL_I. Thelow-pass filter 120 is coupled to the peak detection and bias voltageadjustment circuit 110, and the feedback control circuit is coupled tothe low-pass filter 120 and coupled to the terminals XTAL_I and XTAL_IO.The architecture shown in FIG. 1 adopts some types of Metal OxideSemiconductor Field Effect Transistors (MOSFETs), such as P-type andN-type MOSFETs, but the present invention is not limited thereto.

As shown in FIG. 1, the peak detection and bias voltage adjustmentcircuit 110 may comprise an operational transconductance amplifier (OTA)OTA1, a transistor M0 (such as an N-type MOSFET) and a capacitor C0coupled between the bias current IBias and the ground voltage VSS, and acapacitor C1 coupled between the node N_(B) and the terminal XTAL_I. Theoperational transconductance amplifier OTA1 comprises a first positiveinput terminal, a first negative input terminal and a first outputterminal (e.g. the terminals denoted with “+” and “−” on the left sidethereof and the terminal on the right side thereof, respectively),wherein the first positive input terminal is coupled to the bias currentIBias, the first negative input terminal and the first output terminalare coupled to each other and are both coupled to the node N_(B), andthe control terminal (e.g. the gate terminal) of the transistor M0 maybe coupled to the node N_(B). In addition, the low-pass filter 120 maycomprise the operational transconductance amplifier OTA2, and maycomprise the capacitor C2 coupled between the node N_(D) and the groundvoltage VSS. The operational transconductance amplifier OTA2 comprises asecond positive input terminal, a second negative input terminal and asecond output terminal (e.g. the terminals denoted with “+” and “−” onthe left side thereof and the terminal on the right side thereof,respectively), wherein the second positive input terminal is coupled tothe node N_(B), and the second negative input terminal and the secondoutput terminal are coupled to each other and are both coupled to thenode N_(D). Further, the feedback control circuit may comprise theoperational transconductance amplifier OTA3, the capacitor Cc coupledbetween the node N_(A) and the terminal XTAL_I, the transistors M1 andM2 coupled between the power supply voltage VDD and the ground voltageVSS and located on a first current path, and the transistors M3 and M4coupled between power supply voltage VDD and the ground voltage VSS andlocated on a second current path. The first current path may be thecurrent path passing through the transistors M2 and M1 from top tobottom, and the second current path may be the current path passingthrough the transistors M3 and M4 from top to bottom. The operationaltransconductance amplifier OTA3 comprises a third positive inputterminal, a third negative input terminal and a third output terminal(e.g. the terminals denoted with “+” and “−” on the right side thereofand the terminal on the left side thereof, respectively), wherein thethird positive input terminal is coupled to the terminal XTAL_IO, andthe third negative input terminal and the third output terminal arecoupled to each other and are both coupled to the node N_(A). Thecontrol terminal of the transistor M1 (such as the gate terminalthereof) is coupled to the low-pass filter 120, and two terminals ofmultiple terminals of the transistor M2 are coupled to each other,making the transistor M2 be configured into a dual-terminal component,such as a diode-connected transistor. The multiple terminals of thetransistor M2 may comprise a source terminal, a gate terminal and adrain terminal, wherein the gate terminal and the drain terminal ofthese terminals are coupled to each other. The control terminal of thetransistor M3 (such as the gate terminal thereof) is coupled to thecontrol terminal of the transistor M2 (such as the gate terminalthereof), and the control terminal of the transistor M4 (such as thegate terminal thereof) is coupled to the node N_(A).

According to this embodiment, the terminals XTAL_I and XTAL_IO may bearranged to couple the crystal oscillator control circuit 100 to acrystal, and the peak detection and bias voltage adjustment circuit 110may be arranged to perform peak detection and bias voltage adjustment,in order to correspondingly generate a first signal (such as signalV_(B)) at the node N_(B). In addition, the low-pass filter 120 may becoupled to the node N_(B), and may be arranged to perform low-passfiltering on the first signal (such as the signal V_(B) on the nodeN_(B)) in order to generate a filtered signal (such as signal V_(D)) atthe node N_(D). Further, the control terminal of the transistor M1 (suchas the gate terminal thereof) receives the filtered signal (such assignal V_(D) on the node N_(D)). The feedback control circuit may bearranged to perform feedback control according to the filtered signal(such as the signal V_(D)) in order to generate an oscillation signal toat least one terminal (e.g. one or more terminals) within the terminalsXTAL_I and XTAL_IO, such as the oscillation signals V_(XTAL_I) andV_(XTAL_IO) on the terminals XTAL_I and XTAL_IO, respectively, but thepresent invention is not limited thereto. As shown in FIG. 1, the gainstage 130 in the feedback control circuit may comprise the operationaltransconductance amplifier OTA3, the transistor M4 and the capacitor Cc,wherein two other terminals of the transistor M3 (such as the sourceterminal and drain terminal thereof) are respectively coupled to thepower supply voltage VDD and the third positive input terminal, and twoother terminals of the transistor M4 (such as the drain terminal andsource terminal thereof) are respectively coupled to the third positiveinput terminal and the ground voltage VSS. The gain stage 130 mayprovide gain and feedback path for generating the aforementionedoscillation signal (such as the oscillation signals V_(XTAL_I) andV_(XTAL_IO) on the terminals XTAL_I and XTAL_IO respectively). Inaddition, the gain stage 130 may utilize the capacitor Cc to performleakage current isolation, and more particularly, to isolate any leakagecurrent at the terminal XTAL_I.

Since the capacitor Cc isolates the gate of the transistor M4 from theterminal XTAL_I, the gain stage 130 will be insensitive to the leakagecurrent of the terminal XTAL_I. The operational transconductanceamplifier OTA3 provides a feedback loop, wherein the bias currentthereof may be adjusted for a high output impedance. Hence, the ACsignal on the terminal XTAL_I may be coupled to the gate of thetransistor M4 without suffering from phase shift and amplitudeattenuation. In addition, the peak detection and bias voltage adjustmentcircuit 110 may adjust the bias current of the operationaltransconductance amplifier OTA1, allowing the AC signal on the terminalXTAL_I to be easily coupled to the node N_(B), and more particularly,the operational transconductance amplifier OTA1 will not introduce a DCshift effect between the nodes N_(C) and N_(B). Further, the low-passfilter 120 may provide a clean signal at the node N_(D) for the gate ofthe transistor M1, thereby indirectly providing a clean bias current forthe transistor M4, and may control the bias current of the operationaltransconductance amplifier OTA2 to be adjusted to minimize (oreliminate) any possible ripple on the node D, but the present inventionis not limited thereto. According to some embodiments, the operationaltransconductance amplifier OTA1 may provide a feedback path.

As illustrated by the architecture shown in FIG. 1, the presentinvention provides a crystal oscillator control circuit, which does notapply any resistor or analog switch, and the crystal oscillator controlcircuit also integrates an AGC loop and leakage isolation capacitor in asame architecture without introducing a side effect. More particularly,the resistor-free and analog switch-free crystal oscillator controlcircuit proposed by the present invention may also solve variousproblems existing in the related art, and thus the present invention canavoid the trade-off between solving existing problems and mitigatingnewly-introduced problems, wherein the novel architecture proposed bythe present invention is insensitive to the leakage current, and canalso avoid the requirement for large feedback resistors. In addition,the present invention is capable of reducing the circuit power, reducingsensitivity to PCB current leakage, and reducing related costs (such asmaterial and manufacturing costs).

FIG. 2 illustrates an example of an oscillation device 10 whichcomprises the crystal oscillator control circuit 100 shown in FIG. 1. Asshown in FIG. 2, the oscillation device 10 may further comprise thecrystal coupled between the terminals XTAL_I and XTAL_IO, and a firstcapacitor and a second capacitor coupled to the terminals XTAL_I andXTAL_IO, respectively. For example, the upper terminals of the firstcapacitor and the second capacitor are coupled to the terminals XTAL_Iand XTAL_IO respectively, and the lower terminals of the first capacitorand the second capacitor are coupled to ground.

Based on the architecture shown in FIG. 1 and FIG. 2, the crystaloscillator control circuit and oscillation device of the presentinvention avoid using resistors and analog switches. More particularly,the crystal oscillator control circuit and oscillation device with noresistor and analog switch as provided by the present invention cancompletely solve various problems encountered in the related arts.

FIG. 3 illustrates some examples of related signals of the crystaloscillator control circuit 100 shown in FIG. 1, such as the oscillationsignal V_(XTAL_I), the signals V_(C) and V_(D), and the current I_(M3)of the transistor M3, but the present invention is not limited thereto.Regarding the initialization, at the beginning of powering on of thecrystal oscillator control circuit 100, the bias current of thetransistor M4 may be determined by the bias current IBias and transistorratio, wherein a relatively large current may be used for a betterstartup. When the oscillation amplitude of the aforementionedoscillation signal (such as the oscillation signals V_(XTAL_I) andV_(XTAL_IO) on the terminals XTAL_I and XTAL_IO, respectively)increases, the DC voltage on the node N_(C) decreases, and thus the DCvoltage on the node N_(B) also decreases. The operationaltransconductance amplifier OTA2 and the capacitor C2 may allow the DCsignal on the node N_(B) to pass, but attenuate the AC signal. Hence,the signal V_(D) on the node N_(D) may have a decreasing voltage that isslowly changed. In this way, when the oscillation amplitude increases,the bias current of the transistor M4 decreases. Finally, the variationsof the related signals may reach a balance point. As a result, theaforementioned oscillation signal (such as the oscillation signalsV_(XTAL_I) and V_(XTAL_IO) on the terminals XTAL_I and XTAL_IO,respectively) may continue oscillating and the bias current may remainconstant.

According to some embodiments, the crystal oscillator control circuit100 shown in FIG. 1 and the oscillation device 10 shown in FIG. 2 areapplicable to associated designs of various products, such as that of acrystal oscillator (XOSC), phase-locked loop (PLL), clock, and so on.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A crystal oscillator control circuit, comprising:a first terminal and a second terminal, arranged to couple the crystaloscillator control circuit to a crystal; a current source, coupled to apower supply voltage, the current source arranged to generate a biascurrent; a peak detection and bias voltage adjustment circuit, coupledbetween the bias current and a ground voltage and coupled to the firstterminal, wherein the peak detection and bias voltage adjustment circuitis arranged to perform peak detection and bias voltage adjustment inorder to correspondingly generate a first signal at a node; a low-passfilter, coupled to the node, the low-pass filter arranged to low-passfilter the first signal in order to generate a filtered signal; and afeedback control circuit, coupled to the low-pass filter and coupled tothe first terminal and the second terminal, the feedback control circuitarranged to perform feedback control according to the filtered signal,in order to generate an oscillation signal at one or both of the firstterminal and the second terminal; wherein the peak detection and biasvoltage adjustment circuit comprises: a first operationaltransconductance amplifier (OTA), comprising a first positive inputterminal, a first negative input terminal and a first output terminal,wherein the first positive input terminal is coupled to the biascurrent, and the first negative input terminal and the first outputterminal are coupled to each other and are coupled to the node.
 2. Thecrystal oscillator control circuit of claim 1, wherein the peakdetection and bias voltage adjustment circuit further comprises: atransistor, coupled between the bias current and the ground voltage,wherein a control terminal of the transistor is coupled to the node; anda capacitor, coupled between the bias current and the ground voltage. 3.The crystal oscillator control circuit of claim 2, wherein the peakdetection and bias voltage adjustment circuit further comprises: anothercapacitor, coupled between the node and the first terminal.
 4. Thecrystal oscillator control circuit of claim 1, wherein the low-passfilter comprises: a second operational transconductance amplifier (OTA),comprising a second positive input terminal, a second negative inputterminal and a second output terminal, wherein the second positive inputterminal is coupled to the node, and the second negative input terminaland the second output terminal are coupled to each other and are coupledto another node; wherein the low-pass filter generates the filteredsignal at the other node.
 5. The crystal oscillator control circuit ofclaim 4, wherein the low-pass filter further comprises: a capacitor,coupled between the other node and the ground voltage.
 6. The crystaloscillator control circuit of claim 1, wherein the feedback controlcircuit comprises: a third operational transconductance amplifier (OTA),comprising a third positive input terminal, a third negative inputterminal and a third output terminal, wherein the third positive inputterminal is coupled to the second terminal, and the third negative inputterminal and the third output terminal are coupled to each other and arecoupled to another node; and a capacitor, coupled between the other nodeand the first terminal.
 7. The crystal oscillator control circuit ofclaim 6, wherein the feedback control circuit comprises: a firsttransistor and a second transistor, coupled between the power supplyvoltage and the ground voltage, and located on a first current path,wherein a control terminal of the first transistor is coupled to thelow-pass filter in order to receive the filtered signal, and twoterminals among multiple terminals of the second transistor are coupledto each other, configuring the second transistor into a dual-terminalcomponent; and a third transistor and a fourth transistor, coupledbetween the power supply voltage and the ground voltage, and located ona second current path, wherein a control terminal of the thirdtransistor is coupled to a control terminal of the second transistor,and a control terminal of the fourth transistor is coupled to the othernode.
 8. The crystal oscillator control circuit of claim 7, wherein again stage in the feedback control circuit comprises: the third OTA,wherein two other terminals of the third transistor are coupled to thepower supply voltage and the third positive input terminal,respectively; the fourth transistor, wherein two other terminals of thefourth transistor are coupled to the third positive input terminal andthe ground voltage, respectively; and the capacitor; wherein the gainstage provides gain and a feedback path for generating the oscillationsignal, and utilizes the capacitor to perform leakage current isolation.9. An oscillation device comprising the crystal oscillator controlcircuit of claim 1, wherein the oscillation device further comprises:the crystal, coupled between the first terminal and the second terminal;and a first capacitor and a second capacitor, coupled to the firstterminal and the second terminal, respectively.
 10. A crystal oscillatorcontrol circuit, comprising: a first terminal and a second terminal,arranged to couple the crystal oscillator control circuit to a crystal;a current source, coupled to a power supply voltage, the current sourcearranged to generate a bias current; a peak detection and bias voltageadjustment circuit, coupled between the bias current and a groundvoltage and coupled to the first terminal, wherein the peak detectionand bias voltage adjustment circuit is arranged to perform peakdetection and bias voltage adjustment in order to correspondinglygenerate a first signal at a node; a low-pass filter, coupled to thenode, the low-pass filter arranged to low-pass filter the first signalin order to generate a filtered signal; and a feedback control circuit,coupled to the low-pass filter and coupled to the first terminal and thesecond terminal, the feedback control circuit arranged to performfeedback control according to the filtered signal, in order to generatean oscillation signal at one or both of the first terminal and thesecond terminal; wherein the low-pass filter comprises: a secondoperational transconductance amplifier (OTA), comprising a secondpositive input terminal, a second negative input terminal and a secondoutput terminal, wherein the second positive input terminal is coupledto the node, and the second negative input terminal and the secondoutput terminal are coupled to each other and are coupled to anothernode; wherein the low-pass filter generates the filtered signal at theother node.
 11. The crystal oscillator control circuit of claim 10,wherein the low-pass filter further comprises: a capacitor, coupledbetween the other node and the ground voltage.
 12. The crystaloscillator control circuit of claim 10, wherein the feedback controlcircuit comprises: a third operational transconductance amplifier (OTA),comprising a third positive input terminal, a third negative inputterminal and a third output terminal, wherein the third positive inputterminal is coupled to the second terminal, and the third negative inputterminal and the third output terminal are coupled to each other and arecoupled to another node; and a capacitor, coupled between the other nodeand the first terminal.
 13. The crystal oscillator control circuit ofclaim 12, wherein the feedback control circuit comprises: a firsttransistor and a second transistor, coupled between the power supplyvoltage and the ground voltage, and located on a first current path,wherein a control terminal of the first transistor is coupled to thelow-pass filter in order to receive the filtered signal, and twoterminals among multiple terminals of the second transistor are coupledto each other, configuring the second transistor into a dual-terminalcomponent; and a third transistor and a fourth transistor, coupledbetween the power supply voltage and the ground voltage, and located ona second current path, wherein a control terminal of the thirdtransistor is coupled to a control terminal of the second transistor,and a control terminal of the fourth transistor is coupled to the othernode.
 14. The crystal oscillator control circuit of claim 13, wherein again stage in the feedback control circuit comprises: the third OTA,wherein two other terminals of the third transistor are coupled to thepower supply voltage and the third positive input terminal,respectively; the fourth transistor, wherein two other terminals of thefourth transistor are coupled to the third positive input terminal andthe ground voltage, respectively; and the capacitor; wherein the gainstage provides gain and a feedback path for generating the oscillationsignal, and utilizes the capacitor to perform leakage current isolation.15. An oscillation device comprising the crystal oscillator controlcircuit of claim 10, wherein the oscillation device further comprises:the crystal, coupled between the first terminal and the second terminal;and a first capacitor and a second capacitor, coupled to the firstterminal and the second terminal, respectively.